Generally, a washing machine is a machine that washes clothing using electric power, and types of the washing machine include a front-loading washing machine in which a rotating tub is horizontally disposed to wash laundry by lifting the laundry along an inner circumferential surface of the rotating tub and dropping the laundry while rotating the rotating tub rotates about a horizontal axis in forward and reverse directions, and a vertical-axis clothes washing machine in which a rotating tub provided with a pulsator is vertically disposed to wash laundry using a water current generated by the pulsator while rotating the rotating tub about a vertical axis in forward and reverse directions.
Generally, the front-loading washing machine includes a cabinet, a tub configured to store washing water in the cabinet, and a drum configured to accommodate laundry and installed to be rotatable in the tub. The cabinet includes an opening, and the opening is provided to be opened or closed by a door.
When laundry, a detergent, and washing water are inserted into the drum, the drum rotates to mix the laundry with the washing water so that dirt is removed from the laundry.
In this process, the laundry is inserted into the opening provided in the cabinet, and the detergent and the washing water are supplied by a detergent supply device.
However, when a washing cycle of the front-loading washing machine starts, the door of the front-loading washing machine maintains a locked state. Therefore, to open the door during the washing process, a user needs to wait until the washing cycle is finished or stop the washing cycle and wait until a draining of the washing water is finished. Thus, the front-loading washing machine has a problem in that an additional supply of laundry or a detergent to the inside of the drum during the washing process is restricted.